The present invention relates to a diagnosis apparatus for a photo coupler and a photo coupler device with diagnosis function, and more particularly to an apparatus which is capable of diagnosing the deterioration in the function of a photo coupler the light receiving surface of which is liable to be stained by chemicals or the like as in an automatic chemical analysis apparatus.
A typical conventional position detector utilizes a photo coupler such as a photo interrupter in which a light emitting diode and a photo transistor are used as a light emitting element and a light receiving element respectively and light proceeding from the light emitting diode to the photo transistor is interrupted by a detector plate interlocking with a moving body or passed to the photo transistor. Such a photo coupler is disclosed by, for example, the catalog "Series of Photo-Electric Elements" published by Omron Company. A sufficient current always flows through the light emitting diode so as to allow the incidence of light capable of sufficiently saturating the photo transistor, and light from the light emitting diode is interrupted by the detector plate or passed, thereby changing the impedance of the photo transistor to turn the photo transistor on or off. Whether or not the detector plate is in a light interrupting position can be detected on the basis of the ON/OFF output of the photo transistor.
The above-mentioned catalog also discloses a photo coupler using a reflection type of detector plate. In this photo coupler, light from a light emitting diode is reflected by the detector plate and the reflected light is brought onto a photo transistor. A sufficient current is always flown through the light emitting diode so as to sufficiently saturate the photo transistor by the reflected light from the detector plate, and light from the light emitting diode is reflected by the detector plate or passed, thereby turning the phototransistor on or off. Whether or not the detector plate is in a light reflecting position can be detected on the basis of the ON/OFF output of the photo transistor.
In the case where the light emitting diode and the photo transistor are connected in series with each other, a light-activated positive feedback is produced during incidence of light from the light emitting diode upon the photo transistor so that the photo transistor is turned on or a current becomes liable to flow through the photo transistor with the result that a sufficient current continues flowing through the light emitting diode connected in series with the photo diode and hence the photo transistor continues producing its ON output. If, when the photo coupler is in such a state, the detector plate comes to a position at which light from the light emitting diode is not incident upon the photo transistor the photo transistor assumes its Off condition so that a current flowing through the photo transistor becomes approximately zero and hence a current flowing through the light emitting diode connected in series with the photo transistor correspondingly decreases. Thus, the output of the photo transistor is changed in accordance with the position of the detector plate in such a manner that when the light from the light emitting diode does not impinge upon the photo transistor in dependence on the position of the detector plate, a current flowing through the light emitting diode is decreased, thereby reducing the amount of light.
In the above-mentioned prior art, a constant current with which the light emitting diode emits light capable of sufficiently saturating the photo transistor may always flows through the light emitting diode. For the photo coupler in which the light emitting diode and the photo transistor are connected so that the light-activated positive feedback is provided, a current flowing through the light emitting diode when light from the light emitting diode impinges upon the photo transistor is brought to a value with which the light emitting diode emits light capable of sufficiently saturating the photo transistor while the current of the light emitting diode when the light from the light emitting diode does not impinge upon the photo transistor is selected to have the minimum value with which the positive feedback is properly induced upon a point of time when the light enters the photo transistor again. However, no consideration is paid to any deterioration attendant upon the lapse of time including the decrease of the amount of light emitted from the light emitting diode at the same current, the deterioration of a detection level of the photo transistor, and the decrease of the amount of light incident upon the photo transistor resulting from stains on the light emitting surface of the light emitting diode, the light receiving surface of the photo transistor and the light reflecting surface of the reflection type of detector plate by chemicals or the like. Therefore, when such a deterioration gradually progresses, the progression of the deterioration cannot be detected until the deterioration reaches a level at which the detection of a position of the detector plate is impossible and the system becomes inoperative. In a system such as an automatic analysis apparatus using a multiplicity of (50 to 100) photo interrupters, a great problem is how to reduce the rate of inferior photo interrupters, thereby improving the reliability. In the case of a system using many chemicals as in biochemistry, there is a problem that the photo interrupter is liable to be stained with a decreased amount of light incident upon the light receiving element, thereby resulting in frequent troubles due to the inferiority of the photo interrupter.